The present invention provides a pressure relief valve adapted to relieve an overpressure condition at the discharge of a mud pump. A mud pump, typically a triplex pump, delivers a large volume of mud flow for a drilling rig. The mud pump delivers drilling mud to the drill stem to flow down the string of drill pipe and out through the drill bit appended to the lower end of the drill stem. Then, the mud flow returns to the surface for recycling. To carry out its various functions, mud must flow at a substantial flow rate. A mud pump commonly delivers 1,000 gallons per minute through the drill stem at a discharge from the mud pump of 1,000 psi or more.
Any impediment in the flow path of the drilling mud results in an increase in the discharge pressure of the mud pump. In fact, pressure at the discharge of the mud pump will vary during normal operation. If this increase in pressure were to continue without corrective action, substantial damage would result to the mud pump or its associated downstream equipment or both. In U.S. Pat. No. 5,975,129, a hydraulically operated pressure relief valve solved many of these and related problems by providing a valve body including an inlet mud flow opening, an internal passage with a movable valve element to modulate flow, and a mud out let opening for connection to a mud reservoir. The movable valve element connected to a piston rod which was connected to a dual chamber, hydraulically operated, force-creating, air cushioned regulator which adjusted the force on the piston rod and thereby adjusted the position of the valve element. An over pressure condition forced the movable valve element up until a rod extension cleared its seal, permitting the valve to pop open. Hydraulic fluid was then applied to reset the valve to a position ready for subsequent operation.
This pressure relief valve proved very successful, but it required a separate hydraulic actuation and reset system. The present invention improves on that valve by providing a pneumatic setpoint and reset arrangement.